A method for calculating and matching large attitude angle dynamic push-broom line frequency of space-borne TDI detector

Abstract

The application provides a large attitude angle dynamic push-broom line frequency calculation and matching method of a spaceborne TDI detector, and is used for solving the technical problems that the existing image motion velocity vector calculation model does not consider the actual ellipsoid earth shape, calculation errors are introduced in the satellite attitude transformation process, or the actual ellipsoid earth shape is considered, but a large number of matrices, differentials and partial derivatives make the calculation result complex, the calculation speed is slow, and the calculation amount is large. The large attitude angle dynamic push-broom line frequency calculation and matching method of the spaceborne TDI detector considers the ellipsoid earth model and satellite attitude change and the like, combines the vector relationship method and the coordinate transformation method, can accurately calculate the object distance and the downward angle corresponding to each detector center point in the dynamic push-broom process of the camera, and further obtains the image motion velocity on the image plane corresponding to each detector center point; so as to calculate the image motion velocity, the line frequency and the deflection angle corresponding to each detector center point, and complete the line frequency matching.

Description

TECHNICAL FIELD

[0001] The present application relates to a line frequency calculation and matching method, in particular to a kind of star-borne TDI detector large attitude angle dynamic push-broom line frequency calculation and matching method. BACKGROUND

[0002] In recent years, in the field of space remote sensing, with the continuous improvement of ground resolution, the industry is constantly pursuing resolution, and higher requirements are put forward for satellite rapid response capability, observation efficiency and imaging width. Therefore, agile satellite as a new type of earth observation satellite application is born with the characteristics of high efficiency, fast and flexible. At the same time, researchers put forward higher and higher requirements for the resolution, field of view, signal-to-noise ratio, volume and weight of space camera carried by agile satellite.

[0003] At present, time delay integration detector (Time-delay Integration, TDI) as a focal plane device of space camera has become the preferred detector. TDI detector is a kind of area array structure, linear array output detector, with multiple stage delay integration function, through multiple stage photosensitive element to the same target multiple stage integration, each stage integration of weak signal is superimposed as strong signal output, can obtain higher signal-to-noise ratio and sensitivity, greatly improve the image quality. But in the imaging process, due to the influence of earth rotation, satellite attitude maneuver, orbit motion and other factors, the imaging quality is reduced due to the inconsistency of the image shift velocity vector of each image point on the detector focal plane and the transfer velocity vector of charge packet in the process of multi-stage output. Moreover, the more the integration stages, the greater the image shift velocity mismatch, and the worse the imaging quality. Therefore, how to realize image shift compensation for each image point on the detector focal plane, establish accurate image shift velocity vector calculation model, has become the focus of domestic and foreign researchers.

[0004] In 2004, Academician Wang Jiaqi established the nadir point imaging formula by calculating the position equation and the velocity equation of the image plane through the change relationship of the seven coordinate systems of the ground scene to the image plane, and then obtained the calculation formula of the image motion velocity vector; in 2006, Yuan Xiaokang of Shanghai Institute of Satellite Engineering proposed a method for realizing the camera drift angle compensation of satellite yaw control, and obtained the analytical calculation formula of the drift angle and the target image motion velocity in the case of the nadir point and satellite attitude maneuver push-broom imaging; in 2012, Huang Qundong et al. of Space East Red Satellite Co., Ltd. obtained the mathematical analytical expression of the image motion velocity in the dynamic imaging mode by using the coordinate transformation method; however, all these expressions are calculated based on the spherical earth model, without considering the actual ellipsoid earth shape, and thus calculation errors are directly introduced in the satellite attitude transformation process; in 2016, Li Yongchang of Changchun Institute of Optics, Fine Mechanics and Physics established the image motion velocity vector expression based on the ellipsoid earth model and the off-axis three-mirror optical lens, and considered the actual ellipsoid earth shape, but the calculation result is complex, the calculation amount is large and the calculation speed is slow due to a large number of matrices, differentials and partial derivatives. SUMMARY

[0005] The present application aims at the technical problems that the existing image motion velocity vector calculation model does not consider the actual ellipsoid earth shape, calculation errors are introduced in the satellite attitude transformation process, or the actual ellipsoid earth shape is considered, but the calculation result is complex, the calculation speed is slow and the calculation amount is large due to a large number of matrices, differentials and partial derivatives, and provides a large attitude angle dynamic push-broom line frequency calculation and matching method for a spaceborne TDI detector.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A large attitude angle dynamic push-broom line frequency calculation and matching method for a spaceborne TDI detector, which is characterized by comprising the following steps:

[0008] Step 1: establishing an ellipsoid earth model, initializing the parameters of the satellite orbit, the earth and the camera, and defining the coordinate system of the ellipsoid earth model according to the imaging principle of the spaceborne TDI detector; the coordinate system of the ellipsoid earth model comprises a geocentric equatorial inertial coordinate system, a satellite orbit coordinate system, a satellite body coordinate system, a space camera coordinate system and a camera focal plane coordinate system;

[0009] Step 2: calculating the inverse matrix of the conversion matrix of the geocentric equatorial inertial coordinate system and the satellite orbit coordinate system the inverse matrix of the conversion matrix of the satellite orbit coordinate system and the satellite body coordinate system and the inverse matrix of the camera installation matrix establishing the ellipsoid geometric relationship constraint equation corresponding to the space camera coordinate system and the camera focal plane coordinate system, and combining the obtained matrix matrix and matrix calculating the position vector between the camera coordinate origin and the target point;

[0010] Step 3, calculating the included angle between the line connecting the center point of each detector in the space-borne TDI detector and the camera coordinate origin and the line connecting the center point of the focal plane of the space-borne TDI detector and the camera coordinate origin, and then calculating the down-view angle corresponding to each detector center point when the satellite attitude angle changes; and then combining the position vector between the camera coordinate origin and the target point obtained in Step 2, calculating the object distance corresponding to each detector center point;

[0011] Step 4, converting the absolute velocity vector of the target point caused by the earth rotation and the relative velocity vector of the target point caused by the satellite motion into the space camera coordinate system, calculating the image motion velocity on the image plane corresponding to each detector center point in the space camera coordinate system; and then combining the object distance obtained in Step 3, calculating the image motion velocity on the image plane corresponding to each detector center point;

[0012] Step 5, when the satellite attitude is maneuvered for push-broom imaging, calculating the ground push-broom velocity of the camera when the camera push-broom trajectory and the camera subspace point trajectory are at different included angles;

[0013] Step 6, according to the image motion velocity on the image plane corresponding to each detector center point obtained in Step 4 and the ground push-broom velocity of the camera obtained in Step 5, calculating the image motion velocity, the line frequency and the deflection angle corresponding to each detector center point when the satellite attitude is maneuvered for push-broom imaging;

[0014] Step 7, according to the image motion velocity, the line frequency and the deflection angle corresponding to each detector center point when the satellite attitude is maneuvered for push-broom imaging calculated in Step 6, determining the change curve of the modulation transfer function, and then completing the line frequency matching through the change curve of the modulation transfer function.

[0015] Further, in Step 2, the inverse matrix of the conversion matrix between the geocentric equatorial inertial coordinate system and the satellite orbit coordinate system is calculated by the following formula

[0016]

[0017] The inverse matrix of the conversion matrix between the satellite orbit coordinate system and the satellite body coordinate system is calculated by the following formula

[0018]

[0019] The inverse matrix of the camera installation matrix is calculated by the following formula

[0020]

[0021] Wherein, u is the satellite latitude amplitude angle, Ω is the orbit ascending node right ascension, i is the orbit inclination, ψ is the satellite yaw angle, is the satellite yaw angle, θ is the satellite pitch angle.

[0022] Further, in step 2, the ellipsoid geometric relationship constraint equation corresponding to the space camera coordinate system and the camera focal plane coordinate system is established, and the obtained matrix Matrix And the matrix The position vector between the camera coordinate origin and the target point is calculated as follows:

[0023] Step a, the ellipsoid geometric relationship constraint equation corresponding to the space camera coordinate system and the camera focal plane coordinate system is established, and the expression is as follows:

[0024]

[0025] In the formula, X I , Y I , Z I are the components of the position vector between the camera coordinate origin and the target point in three directions, is the vector of the camera coordinate origin pointing to the ground target point in the space camera coordinate system, is the relative position vector of the camera coordinate origin and the satellite coordinate origin in the satellite body coordinate system, that is, the installation position of the camera, is the translation vector, r is the satellite orbit geocentric distance, r=R e +H0, R e is the average earth radius, H0 is the orbit height; p1, p2 are the horizontal coordinate and vertical coordinate of the focal plane position vector respectively, f is the camera focal length, a e is the earth long semi-axis, b e is the earth short semi-axis; X c , T c , Z c are the components of the position vector between the camera coordinate origin and the target point in three directions;

[0026] Step b, according to the geometric relationship constraint equation corresponding to the space camera coordinate system and the camera focal plane coordinate system, X c , Y c , Z c are solved, and the position vector between the camera coordinate origin and the target point is obtained.

[0027] Further, in step 3, the angle between the line connecting the center point of each detector segment and the origin of the camera coordinate system in the spaceborne TDI detector and the line connecting the center point of the focal plane of the spaceborne TDI detector and the origin of the camera coordinate system is calculated using the following formula:

[0028] ag i =arc tan(S i *p s *pixels / f)

[0029] In the formula, ag i Let S be the angle between the line connecting the center point of the i-th detector in the spaceborne TDI detector and the origin of the camera coordinate system, and the line connecting the center of the focal plane of the TDI detector and the origin of the camera coordinate system, where i = 1, 2, ..., N, and N is the total number of detectors in the spaceborne TDI detector. i Let ps be the center point of the i-th detector, ps be the pixel size, and pixels be the pixel size.

[0030] Furthermore, in step 3, the center point position S of each detector... i The formula for determining it is:

[0031] S i =-N / 2+0.5, -N / 2+1.5,..., N / 2-0.5.

[0032] Furthermore, in step 3, the downward angle α corresponding to the center point of the i-th detector is calculated using the following formula when the satellite attitude angle changes. i :

[0033]

[0034] The object distance L corresponding to the center point of the i-th detector is calculated using the following formula. i :

[0035]

[0036] Furthermore, step 4 specifically involves:

[0037] Step 4.1, calculate the absolute velocity vector v of the target point caused by the Earth's rotation. a The velocity vector v of the target point caused by the satellite's motion e All are transformed to the space camera coordinate system, combined with formula v r =v a -v e Calculate the image displacement velocity corresponding to the center point of the i-th detector in the space camera coordinate system.

[0038] Step 4.2, calculate the image displacement velocity v on the image plane corresponding to the center point of the i-th detector according to the following formula.i :

[0039]

[0040] Further, in step 5, the ground push-broom speed v of the camera when the push-broom trajectory of the camera is different from the subspace point trajectory of the camera is calculated by the following formula ηi :

[0041]

[0042] In the formula, w η is the push-broom angular velocity of the camera, β i is the geocentric angle corresponding to the i-th piece of the detector,

[0043] Further, in step 6, the image motion speed V i , the line frequency f TDIi and the deflection angle alpha_d i corresponding to the center point of the i-th piece of the detector during the satellite attitude maneuver push-broom imaging are respectively calculated by the following formula

[0044]

[0045] Further, in step 7, the change curve MTF of the modulation transfer function is determined by the following formula

[0046]

[0047] In the formula, Δv=V m -V i , under the condition of the same speed, V m is the image motion speed of the center point of the TDI detector focal plane, V i is the image motion speed of the center point of each piece of the detector; under the condition of different speeds, V m is the image motion speed of the edge of each piece of the detector.

[0048] The beneficial effects of the present application compared with the prior art are as follows:

[0049] 1. The satellite-borne TDI detector large attitude angle dynamic push-broom line frequency calculation and matching method provided by the present application considers the influence of the ellipsoid earth model, satellite attitude change and the like, and can accurately calculate the object distance and the downward angle corresponding to the center point of each piece of the detector on the TDI detector during the dynamic push-broom process of the camera by combining the vector relationship method and the coordinate transformation method, and further obtain the accurate image motion speed on the image plane; the calculation process of the method of the present application is simpler, the calculation speed is fast, the component expression is clear and analyzable, and the engineering application is easier to realize.

[0050] 2. The application provides a large attitude angle dynamic push-broom line frequency calculation and matching method for a spaceborne TDI detector, which realizes high-precision matching of the large field angle spaceborne TDI detector under large attitude angle conditions by analyzing the change curve of the modulation transfer function and determining the real-time frequency modulation of the single detector. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 A flowchart of the large attitude angle dynamic push-broom line frequency calculation and matching method for the spaceborne TDI detector embodiment of the application is shown in the figure.

[0052] Figure 2 A parameter relationship diagram during satellite attitude change push-broom imaging in step 6 of the embodiment of the application is shown in the figure.

[0053] Figure 3 A calculation result diagram of the image motion speed difference in step 7 of the embodiment of the application is shown in the figure, wherein (a) is a calculation result diagram of the image motion speed difference under the same speed condition, and (b) is a calculation result diagram of the image motion speed difference under the different speed condition of one line frequency for one piece.

[0054] Figure 4 The figure is a modulation transfer function change curve of the subsatellite point, wherein the red curve represents the modulation transfer function change curve under the same speed condition, and the blue curve represents the modulation transfer function change curve under the different speed condition.

[0055] Figure 5 The figure is a modulation transfer function change curve of the 30° side swing, wherein the red curve represents the modulation transfer function change curve under the same speed condition, and the blue curve represents the modulation transfer function change curve under the different speed condition.

[0056] Figure 6 The figure is a modulation transfer function change curve of the 45° side swing, 30° pitch, and-0.5° pitch angular velocity, wherein the red curve represents the modulation transfer function change curve under the same speed condition, and the blue curve represents the modulation transfer function change curve under the different speed condition. DETAILED DESCRIPTION

[0057] In order to make the advantages and characteristics of the application clearer, the application is further described in detail below in combination with the drawings and specific embodiments.

[0058] A large attitude angle dynamic push-broom line frequency calculation and matching method for a spaceborne TDI detector, as shown in the figure, specifically includes the following steps. Figure 1

[0059] Step 1: An ellipsoid earth model is established, the parameters of the satellite orbit, the ellipsoid earth model and the camera are initialized, and the coordinate system of the ellipsoid earth model is defined.

[0060] ​Step 1.1, the initialized satellite orbit parameters include: orbit ascending node right ascension Ω, orbit inclination i, satellite latitude amplitude angle u, orbit height H0, terrain height h, satellite angular velocity w along the orbit a , sub-satellite point latitude γ, satellite yaw angle satellite pitch angle θ, satellite yaw angle ψ, satellite yaw angular velocity satellite pitch angular velocity satellite yaw angular velocity time t.

[0061] The initialized ellipsoidal earth model parameters include: earth major axis a e , earth minor axis b e , average earth radius R e , earth rotation angular velocity w e .

[0062] The initialized camera parameters include: camera focal length f, integration order M, installation position focal plane position vector and installation matrix M cb .

[0063] The initialized values of some parameters of the satellite orbit, the earth and the camera in this embodiment are shown in Table 1, and the initialized values of the parameters not shown in Table 1 are all 0.

[0064] Table 1 initialized values of some parameters of the satellite orbit, the earth and the camera

[0065]

[0066]

[0067]

[0068] Step 1.2, according to the principle of space-borne TDICMOS imaging, the coordinate system of the ellipsoidal earth model is defined, which specifically includes:

[0069] (1) the geocentric equatorial inertial coordinate system: O e -x I y I z I , abbreviated as I system;

[0070] The coordinate system origin of the I system is the geocenter O e , O e x I is located in the equatorial plane, pointing to the J2000.0 vernal equinox, O e z I is perpendicular to the equatorial plane, pointing to the north pole, and is consistent with the direction of the earth's rotation angular velocity vector, O e yI Perpendicular to O e x I , O e z I Two coordinate axes.

[0071] (2) Satellite orbit coordinate system: O s -x o y o z o , abbreviated as o system;

[0072] The coordinate system origin of the o system is located at the satellite center of mass O s , O s x o is located in the satellite orbit plane, pointing to the satellite motion direction, O s z o points to the Earth's center O e , O s y o is perpendicular to O s x o and O s z o coordinate axis, respectively, this coordinate system makes an orbital motion in the I system with the satellite's angular velocity.

[0073] (3) Satellite body coordinate system: O s -x b y b z b , abbreviated as b system;

[0074] The coordinate system origin of the b system is located at the satellite center of mass O s , coincides with the origin of the o system, when the satellite has no attitude motion, O s x b , O s y b , O s z b completely corresponds to the coordinate axis in the o system, the three-axis attitude of the satellite is the three-axis attitude of the b system in the o system. O s x b , O s y b , O s z b are the roll, pitch, and yaw axes of the satellite attitude motion, respectively.

[0075] (4) Space camera coordinate system: O c -x c y c z c , abbreviated as c system;

[0076] The coordinate system origin of the c system is the camera imaging center, the optical system principal point Oc c z c is a ground target point in the direction of the optical axis, c x c , O c y c in the plane of the camera objective.

[0077] (5) Camera focal plane coordinate system: O p -x p y p z p , abbreviated as p system;

[0078] The origin of the coordinate system of the p system is the focal plane center O p , O p x p is located in the camera focal plane, parallel to the O c x c axis, along the TDI integration direction, O p y p is located in the camera focal plane, perpendicular to the TDI integration direction, parallel to the O c y c axis, O p z p is the focal plane normal, the same as the O c z c axis direction.

[0079] Step 2, obtain the position vector between the camera coordinate origin and the target point.

[0080] Step 2.1, after substituting the data in step 1, calculate the inverse matrix of the conversion matrix of the I system and the o system respectively by the following formula the inverse matrix of the conversion matrix of the o system and the b system and the inverse matrix of the camera installation matrix

[0081]

[0082] Step 2.2, for the ellipsoidal earth model, establish the geometric relationship constraint equation corresponding to the c system and the p system, solve the geometric relationship constraint equation corresponding to the c system and the p system, and obtain the position vector between the camera coordinate origin and the target point

[0083] Specifically, the geometric relationship constraint equation expression corresponding to the c system and the p system is:

[0084]

[0085] In the formula, X I , Y I , Z​I are target point position vectors respectively are components of the three directions respectively, is a vector from the camera coordinate system origin to the target point on the ground, is a relative position vector of the camera coordinate system origin and the satellite coordinate system origin in the satellite body coordinate system, i.e. the installation position of the camera, is a translation vector, r is the geocentric distance of the satellite orbit, r = R e + H0, R e is the average earth radius, H0 is the orbit height; p1, p2 are the horizontal and vertical coordinates of the focal plane position vector respectively, X c , Y c , Z c are position vectors between the camera coordinate system origin and the target point respectively are components of the three directions respectively.

[0086] Step 3, calculate the downward angle and object distance corresponding to the center point of each slice of the detector.

[0087] Step 3.1, in this embodiment, the number of slices N of the detector in the satellite-borne TDI detector is 15, then the positions corresponding to the center points of each slice of the detector are-7, -6,..., 7 in turn, the pixel size ps is 10 μm, and the pixel size pixels is 1200.

[0088] The angle between the line connecting the center point of the i-th slice of the detector in the satellite-borne TDI detector and the camera coordinate system origin and the line connecting the center point of the TDI detector focal plane and the camera coordinate system origin is calculated according to the following formula, as shown in formula (3): Figure 2

[0089] ag i = arctan (S i * ps * pixels / f)

[0090] In the formula, ag i is the angle between the line connecting the center point of the i-th slice of the detector in the satellite-borne TDI detector and the camera coordinate system origin and the line connecting the center point of the TDI detector focal plane and the camera coordinate system origin, i = 1, 2,..., N, S i is the position of the center point of the i-th slice of the detector.

[0091] ​The angle between the line connecting the center points of the 15 detectors and the line connecting the center points of the TDI detector focal plane and the camera coordinate origin in this embodiment is-0.0034, -0.0029, -0.0024, -0.0019, -0.0014, -0.0010, -0.0005, 0, 0.0005, 0.001, 0.0014, 0.0019, 0.0024, 0.0029, 0.0034, respectively.

[0092] Step 3.2, when the satellite attitude angle changes, the downward angle α of the center point of the 15 detectors i According to the formula The calculation is 0.9084, 0.9089, 0.9093, 0.9098, 0.9103, 0.9108, 0.9113, 0.9117, 0.9122, 0.9127, 0.9132, 0.9137, 0.9141, 0.9146, 0.9151, respectively.

[0093] Step 3.3, the object distance L corresponding to the center point of each detector i Through the formula The calculation is 875770.1625, 876450.6872, 877132.6663, 877816.1042, 878501.0053, 879187.3741, 879875.2151, 880564.5328, 881255.3316, 881947.6162, 882641.3911, 883336.6609, 884033.4302, 884731.7035, 885431.4856, respectively.

[0094] Step 4, calculate the image motion speed v corresponding to the center point of each detector in the space camera coordinate system ri And the image motion speed v on the image plane i .

[0095] Step 4.1, according to the traditional photographic ground speed, there is the following formula:

[0096] v r = v a -v e

[0097] In the formula, v a is the absolute speed vector of the target point D caused by the earth rotation, v a = w e × R e , v e is the relative speed vector caused by the satellite motion, v e = wa xR e , v r is the image motion velocity in the space camera coordinate system.

[0098] The absolute velocity vector v a of the target point caused by the earth rotation and the relative velocity vector v e of the target point caused by the satellite motion are both converted to the space camera coordinate system, and the image motion velocity v

[0099] Step 4.2, the image motion velocity v i on the image plane corresponding to each detector center point is calculated according to the formula and the calculation results are as follows: 0.1727, 0.1726, 0.1724, 0.1723, 0.1721, 0.1720, 0.1718, 0.1717, 0.1715, 0.1714, 0.1712, 0.1711, 0.1709, 0.1708, 0.1706.

[0100] Step 5, the ground push-broom velocity of the camera during the satellite attitude maneuver push-broom imaging is calculated.

[0101] When the push-broom trajectory of the camera and the subspace point trajectory of the camera are at different angles η, the ground push-broom velocity v ηi of the camera is calculated by the formula , wherein w η is the push-broom angular velocity of the camera, β i is the geocentric angle corresponding to the i-th detector, and In this embodiment, the geocentric angles corresponding to the 15 detectors are as follows: 1.113, 1.114, 1.115, 1.116, 1.117, 1.117, 1.118, 1.119, 1.12, 1.121, 1.122, 1.123, 1.124, 1.125, 1.126.

[0102] Correspondingly, the ground push-broom velocity v of the camera is as follows: -17281.45, -17328.29, -17375.42, -17422.86, -17470.58, -17518.62, -17566.96, -17615.61, -17664.58, -17713.86, -17763.45, -17813.38, -17863.62, -17914.20, -17965.11.

[0103] Step 6, as Figure 2The diagram shows the parameter relationships during satellite attitude maneuvering pushbroom imaging. The image displacement velocity V corresponding to the center point of each detector during satellite attitude maneuvering pushbroom imaging is calculated using the following formula. i Line frequency f TDIi and deflection angle alpha_d i :

[0104]

[0105] In this embodiment, the image movement velocities corresponding to the center points of the 15 detectors are as follows:

[0106]

[0107] Step 7: Based on the line frequency results obtained in Step 6, i.e., the image displacement velocity V corresponding to the center point of each detector during satellite attitude maneuver pushbroom imaging. i Line frequency f TDIi and deflection angle alpha_d i The modulation transfer function (MTF) curve is determined, and then line frequency matching is completed using the MTF curve.

[0108] In this invention, the modulation transfer function (MTF) variation curve is determined by the following formula:

[0109]

[0110] In the formula, Δv is the image displacement velocity difference, Δv=V m -V i Under the same speed conditions, V m V is the image displacement velocity at the center point of the focal plane of the TDI detector. i Let V be the image displacement velocity at the center point of each detector, under allotropic conditions. m For the edge image movement velocity of each detector piece. For example... Figure 3 As shown in (a), this is a schematic diagram for calculating the image velocity difference Δv under the same velocity conditions. Figure 3 (b) is a schematic diagram for calculating the image shift velocity difference Δv of a single line frequency under allotropic conditions.

[0111] like Figure 4 The figure shows the modulation transfer function variation curve of the sub-satellite point in this embodiment. Figure 5 This is the modulation transfer function variation curve when the side swing angle is 30° in this embodiment. Figure 6 The curves showing the modulation transfer function changes in this embodiment are as follows: yaw angle 45°, pitch angle 30°, and pitch velocity -0.5°. Figures 4-6The middle red curve represents the modulation transfer function curve under the same speed condition, and the blue curve represents the modulation transfer function curve under the different speed condition. It can be seen that the line frequency matching accuracy under the different speed condition is higher than that under the same speed condition, which can guide the line frequency matching of the satellite in the on-orbit process.

[0112] The above is only used to illustrate the technical solutions of the present application, but not to limit it. For ordinary skilled in the art, the specific technical solutions recorded in the above examples can be modified, or some technical features can be replaced equivalently, and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions protected by the present application.

Claims

1. A method for calculating and matching large attitude angle dynamic push-broom line frequency of a space-borne TDI detector, characterized in that, The method comprises the following steps: Step 1, an ellipsoid earth model is established, parameters of satellite orbit, earth and camera are initialized, and a coordinate system of the ellipsoid earth model is defined according to the imaging principle of the satellite-borne TDI detector; the coordinate system of the ellipsoid earth model comprises a geocentric equatorial inertial coordinate system, a satellite orbit coordinate system, a satellite body coordinate system, a space camera coordinate system and a camera focal plane coordinate system; Step 2, calculate the inverse matrix of the conversion matrix between the terrestrial equatorial inertial coordinate system and the satellite orbit coordinate system respectively the inverse matrix of the conversion matrix between the satellite orbit coordinate system and the satellite body coordinate system and the inverse matrix of the camera installation matrix establish the ellipsoid geometric relationship constraint equation corresponding to the space camera coordinate system and the camera focal plane coordinate system, combined with the obtained matrix matrix and matrix calculate the position vector between the camera coordinate origin and the target point; Step 3, an angle between a line connecting a center point of each piece of the satellite-borne TDI detector and the camera coordinate origin and a line connecting a focal plane center point of the satellite-borne TDI detector and the camera coordinate origin is calculated, and then a corresponding down-view angle of each piece of the detector center point when the satellite attitude angle changes is calculated; in combination with the position vector between the camera coordinate origin and the target point obtained in step 2, a corresponding object distance of each piece of the detector center point is calculated; Step 4, the absolute velocity vector of the target point caused by the earth rotation and the relative velocity vector of the target point caused by the satellite motion are both converted into the space camera coordinate system, and a corresponding image motion velocity of each piece of the detector center point in the space camera coordinate system is calculated; in combination with the object distance obtained in step 3, a corresponding image motion velocity on the image plane of each piece of the detector center point is calculated; Step 5, when the satellite attitude maneuver push-broom imaging is performed, a ground push-broom velocity of the camera is calculated when the camera push-broom track and the camera subspace point track are at different angles; Step 6, according to the image motion velocity on the image plane of each piece of the detector center point obtained in step 4 and the ground push-broom velocity of the camera obtained in step 5, a corresponding image motion velocity, line frequency and deflection angle of each piece of the detector center point when the satellite attitude maneuver push-broom imaging is performed are calculated; Step 7, according to the image motion velocity, line frequency and deflection angle of each piece of the detector center point when the satellite attitude maneuver push-broom imaging is performed calculated in step 6, a change curve of the modulation transfer function is determined, and then the line frequency matching is completed through the change curve of the modulation transfer function.

2. The method according to claim 1, wherein: In step 2, the inverse of the transformation matrix from the Earth-Centered-Equatorial Inertial coordinate system to the satellite orbital coordinate system is calculated by The inverse matrix of the conversion matrix of the satellite orbit coordinate system and the satellite body coordinate system is calculated by the following formula The inverse of the camera mounting matrix is calculated by the following formula where u is the satellite latitude amplitude, Ω is the orbit ascending node right ascension, i is the orbit inclination, ψ is the satellite yaw angle, is the satellite yaw angle, θ is the satellite pitch angle.

3. The method according to claim 2, wherein: In step 2, the ellipsoid geometric relationship constraint equation corresponding to the space camera coordinate system and the camera focal plane coordinate system is established, and the obtained matrix Matrix and matrix The position vector between the camera coordinate origin and the target point is calculated as follows: Step a, an ellipsoid geometric relationship constraint equation corresponding to the space camera coordinate system and the camera focal plane coordinate system is established, and the expression is: In the formula, X I Y I Z I These are the target point position vectors. Components in three directions, This is the vector pointing from the camera origin to the ground target point in the space camera coordinate system. This is the relative position vector between the camera's coordinate origin and the satellite's coordinate origin in the satellite's body coordinate system, i.e., the camera's mounting position. It is a translation vector. r is the geocentric distance of the satellite orbit, r = R e +H0, R e Let H0 be the average Earth radius, p1 and p2 be the x and y coordinates of the focal plane position vector, f be the camera focal length, and a be the focal length. e b is the Earth's semi-major axis e X is the Earth's minor semi-axis; c Y c Z c These are the position vectors between the camera's origin and the target point. Components in three directions; Step b, according to the geometric relationship constraint equation corresponding to the space camera coordinate system and the camera focal plane coordinate system, solve X c , Y c , Z c , obtain the position vector between the camera coordinate origin and the target point 4. The method according to claim 3, wherein: In step 3, the angle between the line connecting the center point of each piece of the satellite-borne TDI detector and the camera coordinate origin and the line connecting the focal plane center point of the satellite-borne TDI detector and the camera coordinate origin is calculated by the following formula: ag i = arctan(S i *ps*pixels / f) where ag i is the angle between the line connecting the center point of the i-th detector in the space-borne TDI detector and the origin of the camera coordinate system and the line connecting the center of the focal plane of the TDI detector and the origin of the camera coordinate system, i = 1, 2, …, N, N being the total number of detectors in the space-borne TDI detector, S i is the position of the center point of the i-th detector, ps is the size of a pixel, and pixels is the size of a pixel.

5. The method according to claim 4, wherein: The center point position S of each detector in step 3 i The determination formula is as follows: S i = -N / 2 + 0.5, -N / 2 + 1.5,..., N / 2 - 0.

5.

6. The method according to claim 4 or 5, wherein: In step 3, the downward angle a corresponding to the center point of the i-th detector when the satellite attitude angle changes is calculated by the following formula i : The object distance L corresponding to the center point of the i-th slice detector is calculated by the following formula i :

7. The method according to claim 6, wherein, Step 4 specifically is: Step 4.1, the absolute velocity vector v of the target point caused by the earth rotation is converted to the space camera coordinate system, and the relative velocity vector v of the target point caused by the satellite motion is converted to the space camera coordinate system, and the image motion velocity v of the i-th detector center point in the space camera coordinate system is calculated according to the formula v = v - v a e r a e ​​​​​ Step 4.2, the image motion velocity v on the image plane corresponding to the i-th slice detector center point is calculated according to the following formula i :

8. The method according to claim 7, wherein: In step 5, the ground push-broom velocity v of the camera when the camera push-broom trajectory and the camera subpoint trajectory are different angles is calculated by the following formula ηi : where w η is the camera push-broom angular velocity, β i is the earth central angle corresponding to the i-th slice of the detector, 9. The method according to claim 8, wherein the method is characterized in that: In step 6, the image motion velocity V corresponding to the center point of the i-th detector in the satellite attitude maneuver push-broom imaging is calculated by the following formula respectively i , line frequency f TDIi , and deflection angle alpha_d i :

10. The method according to claim 9, wherein the method is characterized in that: In step 7, the change curve of the modulation transfer function MTF is determined by the following formula: In the formula, Δv = V m -V i , under the condition of same speed, V m is the image motion speed of the center point of the focal plane of the TDI detector, V i is the image motion speed of the center point of each piece of detector; under the condition of different speeds, V m is the edge image motion speed of each piece of detector.

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